The story centers around the happenings of the emergency room of fictional Clark Street Hospital in Chicago, Illinois and the lives of the doctors who work there. Principal characters include emergency room doctor Howard Sheinfeld, a recently divorced ear, nose, and throat specialist who moonlights at the hospital to keep up with his alimony payments, and his colleague Dr. Eve Sheridan.

While essentially a comedy, E/R also contained dramatic elements stemming from its hospital setting.